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Diesel Tech Questions

Top Tech

Bruce W. Smith
Apr 11, 2018
Photographers: Bruce W. Smith

Cummins O-Ring Advice

QUESTION: I’m looking for information about bolting an O-ringed or fire-ringed cylinder head onto a 5.9L Cummins engine. Big-time cylinder pressure from my truck’s compound-turbocharger setup caused the head gasket to blow. What do you recommend?
Rodney Selby
via email
Photo 2/5   |   Having a machine shop O-ring a Cummins cylinder head helps prevent the head gasket from blowing out when boost pressures exceed 40 psi, which is common on compound-turbocharged setups. The process typically costs approximately $300 and involves machining a groove into the head that aligns with the fire ring of the head gasket, then laying a stainless steel wire into the groove so it protrudes a few thousandths of an inch above the fire deck. (Photo courtesy of Larryspower.com)
ANSWER: One thing you always have to seriously consider is the big increase in cylinder pressures compound turbochargers bring to the table. When boost exceeds 40 psi, which it undoubtedly does with compounds, cylinder-head studs alone will not keep the stock head from lifting and the gasket from blowing out. Bill Allen, manager of Source Automotive and a respected drag racer in the Pacific Northwest, has done a lot of multi-turbo installations for street and strip diesel trucks. Bill says: “Whenever a customer goes to compounds on a street Cummins, we recommend they have the head O-ringed. The stainless-steel wire provides extra clamping force on the head gasket’s fire rings (around each cylinder) so high boost pressures don’t push it out.” To “O-ring” a Cummins head requires machining grooves around each cylinder that align with the fire rings on the head gasket, then tapping a circular wire—the “O-ring” if you will—into the channel so it protrudes a few thousandths of an inch above the deck. When the head is installed, the circular wires embed themselves into the center of the head-gasket fire rings, adding extra sealing power. The size of wire and how much it protrudes depends on who you talk to and how the engine is set up. Bill says Superior typically uses a .051-inch wire with a .014-inch protrusion above the deck for street applications. We’ve been told other performance-diesel shops may have as little as .004 inch sticking out, while others use .041-inch wire with between .007- and .010-inch protrusion. Consult with your local machine shop and diesel-performance centers for recommendations and price details before having the work done. Based on our firsthand experience, we attest that having the head modified this way is money well spent—especially when boost pressures range from 40 to 75 pounds in engines making up to 750 hp. Leave the fire-ring modifications to the hard-core sled pullers and drag racers. Because upgraded fire rings replace those already installed in a head gasket, custom gaskets are required. A fire-ringed Cummins head, which can typically withstand boost pressures greater than 100 psi, won’t do well in a street application, because the constant heat cycles of daily driving tend to crack the fire rings, requiring the work to be done all over again. Machine work for the head and/or block is much more involved than O-ringing a head.

Spoiled to DEF

QUESTION: I own a ’16 GMC Sierra 3500HD dualie with a Duramax LML engine. Is there anything special I should do before storing it in Cleveland, Ohio? I changed the engine oil and filter before parking it along with filling up the tank. I keep a battery tender on it also. What about the diesel-exhaust fluid? Will it spoil or go bad from freezing? I understand it has a shelf life. Is that true?
Scott V.
via email
Photo 3/5   |   Diesel exhaust fluid has a shelf life. DEF expiration dates aren’t usually important until it comes to long-term storage of either the fluid or the vehicle it is used in. Ambient temperatures have a definite effect on shelf life. If the maximum temperature does not exceed approximately 75 degrees Fahrenheit for an extended period of time, the shelf life is two years. Warmer conditions shorten its usable life, as will freezing and very low temps.
ANSWER: It all depends on how long you are keeping the truck in storage and whether or not it’s indoors or outside. The battery tender is must-have equipment. Oregon Fuel Injection’s Mark Gotchall shares these tips for anyone storing a diesel-powered pickup for several months or longer: 1) Diesel-exhaust fluid has a shelf life, so make sure fluid being added has an expiration date (noted on the container) beyond the period the truck will be out of service. 2) Fill the tank, but if you are using bio-fuel, remember it, too, has a limited shelf life, up to about six months. It’s best to not use bio-fuel for long-term diesel vehicle storage. 3) Change the oil and fuel filters prior to storage. 4) Have someone drive the truck at least once a month for 30 to 45 minutes at highway speeds to get all mechanical systems to their operating temperature. This keeps everything lubricated and prevents internal component corrosion. Starting the engine and just letting it idle would be worse than not running it at all. As for DEF, according to experts at Cummins, its shelf life depends on temperature and exposure to sunlight. If stored between 10 and 90 degrees Fahrenheit, shelf life will easily be one year. If the maximum temperature does not exceed approximately 75 degrees for an extended period of time, the shelf life will be two years. There’s a great PDF that covers all sorts of information related to DEF at: www.cumminsfiltration.com/sites/default/files/MB10033.pdf.

Bad Connection

QUESTION: My ’07 Dodge Ram’s Cummins engine is getting harder and harder to start, and when it does, it has a slight miss at idle and there’s a light grayish mist coming out of the tailpipe. It also seems to be down on power, and fuel mileage has slipped some. There are no diagnostic trouble codes. I’m very frustrated by what is causing the engine to act like this.
Scott Stallings
via email
ANSWER: You didn’t mention anything about your truck’s engine being modified, and, while we don’t know the exact gremlin causing the rough-running/hard-starting issue, a good place to begin diagnosing it is by removing any programmer device that’s plugged into the injector harness or custom tune in the ECM. “The first thing we do when diagnosing a truck that comes in with hard-start/idling issues is to return ECM calibration to stock values,” says Source Automotive’s Bill Allen. “Removing any aftermarket electronics resets the timing and fueling maps, which helps us determine whether it’s a tuning issue or a truck problem. What we realize quite often is that it’s an aftermarket electronics issue.” Even if there are no diagnostic trouble codes, it’s always good to start diagnosing with stock ECM settings. Then start the engine and drive the truck to see if the issues are resolved or still exist.

Transfer Case Neutralized

QUESTION: The transfer case in my ’07 Dodge Ram suddenly went into Neutral while we were driving through a foot of fresh snow. I had the truck towed to the nearest town, where the local 4x4 shop thought the problem was a broken shift motor and replaced it. Two weeks later, the same thing happened again, this time while I was driving down the interstate in two-wheel drive. I removed the new motor and bench tested it, and all is good. What else could be causing the transfer case to go into Neutral for no apparent reason?
Scott Marks
via text message
ANSWER: Did you check the wiring-harness connectors for the totally integrated power module (TIPM) on the driver-side fender in the engine bay? Their contacts are notorious for getting corroded, which creates a multitude of odd behaviors and intermittent failures. We’ve heard of all kinds of issues from such failure: the transfer case not functioning properly; dash lights, taillights, foglights, and headlights coming on by themselves or going out while the bulbs are still good; sluggish throttle; horn randomly honking; wipers operating on their own; transmission-shifting issues; and a host of other electronic-controlled items misbehaving. Power for all the vehicle’s electronic components routes through the TIPM. The corrosion issue stems from the lower pins in the plugs not being coated with anything from the factory, so all the road grime and debris that get kicked up eventually makes their way to those contacts, and corrosion sets in. Pull all the wiring harnesses to the TIPM and clean the contacts on the box and harnesses with fast-drying electrical cleaner, then coat the pins with dielectric grease before plugging them back in to prevent further corrosion-related issues.

Duramax L5P Tunes

QUESTION: I just bought an ’18 Chevrolet 3500HD. Most of my work is done in western Colorado towing RV trailers or vehicles on my car hauler. My previous trucks had deleted and tuned Cummins 5.9L and 6.7L engines. This is my first Duramax-powered rig. How long before there are tunes and performance parts available?
Stacy Wright
via email
ANSWER: Your question is one many 6.6L Duramax L5P (in ’17-and-up Chevrolet and GMC trucks) owners ask us. The short answer is: Don’t hold your breath. It appears GM’s ECM calibration wizards have worked hard to lock down the electronics on the newest-generation Duramax. Even the best tune writers are finding it nearly impossible to crack the encryption. Cyber-savvy outsiders say GM’s use of “Diffie-Hellman 2048/SHA-256” software-key management and new-vehicle computer hardware allows them to program and update the access keys (for the ECM/TCM) from production year to year, job to job on the assembly line—even down to individual VINs (via OnStar) on the road. So, if someone does miraculously break a key code (or steal it from GM) and come up with a calibration, GM could quickly and easily update the software without the vehicle owner ever knowing it happened. Changing the encryption security key puts code breakers back at square one, which some cyber security experts say could cost $100M and take about a year to crack a single DH key exchange protocol despite using the fastest computers—and every VIN for L5P-powered trucks has a unique key. Because companies that specialize in providing custom tunes don’t have the computing resources of the NSA, writing performance calibrations for the Duramax L5P engine is not likely to happen any time soon.

K5 Diesel Concerns

QUESTION: How many miles should the typical 6.2L diesel last before needing a major overhaul? I found a ’90 Chevrolet K5 Blazer with 215,000 miles on it that appears to have been well taken care of, and I’m thinking about buying it for my get-around putt-putt. I’ll only be driving it about 10,000 miles a year. Little things like the fuel pump, glow plugs, and injectors aren’t my big concern, it’s the internal rotating parts that worry me most.
Roland McDermott
via email
Photo 4/5   |   The late-model J-code GM 6.2L Detroit diesel V-8 engines found in the HMMWVs made 185 hp and 330 lb-ft torque thanks to the free-flowing intake manifold (shown resting on the engine), header-style exhaust, turned-up fuel pump, and other modifications. We’ve had readers tell us they have put more than 500,000 miles on 6.2L powerplants in their rigs without major issues, and we know of others that are pushing 350,000.
ANSWER: Those final runs of 6.2L engines (the last year of production was 1993) had the better cylinder heads, rocker arms, and accessory drives, and made the best power, with 160 hp and 285 lb-ft in non-military trim. That era’s J-code diesels (found in the HMMWVs) made 185 hp and 330 lb-ft torque thanks in part to the military-grade engines using a freer-flowing intake manifold, header-style exhaust manifolds, and a turned-up fuel pump. As for lifespan, we’ve had readers tell us they’ve put more than 500,000 miles on their trucks’ 6.2L engines without major issues, and we know of others that are pushing 350,000. We covered a complete 6.2L rebuild in October 2005 that included installing a Banks Sidewinder turbo kit, and the owner still drives that pickup every day, trouble-free, in the same manner you are considering. The biggest concerns for the stock engine are the condition of the flywheel, harmonic balancer, and accessory-drive pulley, which are known to fail with age, taking out the crankshaft. The original clips on the oil cooler lines are also prone to coming apart. Replace those items, and your K5 should continue to putt around for a long time.

Lost Boost

QUESTION: I was pulling a mini-excavator on a flat-deck trailer up a long grade with my ’14 Ford F-350 when a bang came from the 6.7L engine and it lost all boost. There doesn’t appear to be anything wrong. No diagnostic trouble codes and no leaks. The engine seems to run fine; it just isn’t making boost.
Jake Wooten
via text
Photo 5/5   |   Ford’s plastic cold-side charge-air-cooler tubes are the weakest components of 6.7L Power Stroke engines, and they should be upgraded to prevent tubes splitting under high-boost loads. Performance replacements are typically stainless steel tubes with upgraded couplings and clamps.
ANSWER: Did you check the plastic charge-air-cooler pipe feeding the intake? It sounds like that cold-side tube from the intercooler to the intake manifold either split, or one of the clamps has failed or is loose. Check both ends and the middle of the tube. Upgrade the plastic stock cold-side pipe with a stainless steel CAC tubing-and-boot kit, such as those offered by companies like Mishimoto, XDP, Rudy’s Performance Parts, and MBRP. It’s a good preventive maintenance upgrade for any 6.7L Power Stroke engine.

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